A gear drive device is known in which a first gear and a second gear are installed with a meshing position of the second gear with respect to the first gear fixed at a predetermined phase (see for example Patent Document 1).
The gear drive device described in Patent Document 1 includes jigs extending beside and parallel to a first shaft and a second shaft of a back case. Inserting the jigs through positioning holes and the like and installing (supporting) the gears in order on the first shaft and the second shaft allows the rotational positions (phase, mesh position) of the gears to be fixed with respect to the back case.
Additionally, a rack and pinion gear drive device is known that effectively prevents interference between the teeth of the rack and the teeth of the pinion (see for example Patent Document 2).
In the gear drive device described in Patent Document 2, the rack teeth aligned in the shaft longitudinal direction are formed in a tooth profile via cut processing of the outer surface of the rack shaft. Thereafter, the edges on both sides of the tooth tip portions in the thickness direction and the edges of the tooth profile formed at both ends in the tooth trace direction are chamfered. The chamfered portion of at least the edge proximal to the tooth tip has a suitable roundness. Accordingly, interference with the pinion teeth can be effectively prevented and thus durability can be improved.